Ion funnels are increasingly being used in mass spectrometers to improve sensitivity. Ion funnels collect diffuse ion plumes from ion sources, utilizing a large entrance, and then focus the ion beam by progressively reducing the inner diameter of the circular apertures. A 180° out-of-phase RF waveform is applied to adjacent circular apertures to confine ions radially and prevent their loss to the electrodes. A DC gradient is applied to create a driving force for ions to be transported through the funnel.
An example of a prior art ion funnel is shown in FIG. 1. The ion funnel 100 consists of a stack of electrodes 110 the inner apertures of which progressively decrease along the funnel. The ion funnel has an entry 150 corresponding with the largest aperture, and an exit 160 corresponding with the smallest aperture. As shown in FIG. 1 the entrance 150 and exit 160 are on a line-of-sight, and the center axis 120 between the electrodes 110 is a straight line with no offset.
Ion plumes that are introduced into the ion funnel are accompanied by expanding gas that contains partially solvated ions, droplets, and neutral particles. In cases where large gas loads enter the funnel from, e.g., multi-inlet or large bore inlets these non-ionic particles have significantly adverse effect on the performance of the ion funnel as well as the ion optics downstream of the ion funnel. These adverse effects lead to non-robust operations and frequent instrument downtime for cleaning ion topics.